PRODUCTS
Truss Uplift

Truss uplift is a condition where the bottom chord of a truss lifts or cambers in the winter and then lowers again in the spring. The movement of the truss is caused when there is a temperature and moisture difference between the top chord and the bottom chord. The wood in the top chord expands with the absorbed moisture from the attic space. The bottom chord remains stable with the heat from the space below. Structurally this is not a problem but it can produce cracks in the tape joint at the ceiling and wall junction on partitions near the center of the truss span. If the truss is connected rigidly to the to the top plate of the partition wall it can even lift the wall revealing a gap under the baseboards.

Two items need to be addressed during construction to prevent problems caused by truss uplift. First the partitions should be connected to the truss bottom chord with a slotted 'L' bracket to allow vertical movement of the truss. Secondly the ceiling drywall should not be connected to the truss within 18" of the partitions. The simple use of 2x6 blocking on top of the 2x4 wall plate will provide a fastening point for the drywall which will stay with the wall. The ceiling drywall will flex from the blocking to the first fastener to the truss. Click on the diagram for a more detailed view of this connection.